Radio Frequency IDentification (RFID) is a method of storing and remotely retrieving data using devices called RFID tags. An RFID tag is a small object that can be attached to a product, animal, or person. RFID tags receive and respond to radio-frequency queries from an RFID reader. RFID tags can be either active or passive Passive tags require no internal power source, whereas active tags require a power source. Active RFID tags have an internal power source, and typically have longer range and larger memories than passive tags.
An RFID system includes several components including mobile tags, tag readers, and application software. The RFID system enables a query to be received by the mobile tag and the tag responds with data. The data is received by an REID reader and processed according to the needs of a particular application. The data transmitted by the tag may provide identification or location information, or specifics about the product tagged, such as price, color, date of purchase.
RF identification (RFID) systems are used to track objects, animals and/or people in a large range of applications. As an example, RFID is used to track books in a library. Security gates includes an RF transceiver as part of the RFID reader which detects whether or not a book has been properly checked out of the library. When the book returns, the tag attached to the book is detected and an appropriate record is updated in the library system. In another application, RFID readers previously located in a warehouse are used to identify certain objects (for example, on a track entering the warehouse), or to find the location of certain objects, by communicating with their tags and measuring the position of their tags.
A RFID system employs tags on various objects and readers of the tags in a given space. The main function of an RFID is to enable identifying the objects and possibly reading and writing data of the objects to and from the respective tags. Often the RFID system allows tracking the location of the objects via the respective tag location.
In certain RFID applications, it is important to ascertain that the identified tag is located within a certain distance from the reader. For example, the identification of the tag may be required in order to open a door to an access-limited area. If a tag which is positioned remotely from the reader is identified by the reader, the door may be opened to an unauthorized individual. Limiting transmission range of the reader is not a potential solution to this problem because near the limit of the transmission range tags may not be identified for instance due to different tag orientations and/or on occlusion between the tag and reader. Ultra-wide band communications is particularly useful for determining distance and location of RFID tags. PCT International Patent Application Publication No. WO 2003/098528, (PCT Patent Application No. PCT/IL2003/00358), entitled “Method and system for distance determination of RF tags” is incorporated by reference for all purposes as if fully set forth herein. PCT/IL2003/00358 discloses an RFID system having the capability of automatically identifying unknown tags by sending a broadcast interrogation ultra wide-band (UWB) message signal and receiving responses from tags that receive the message signal.
As known in the art of RFID systems, the Readers are devices which identify and concentrate the data from the tags. An RFID system is a useful tool to obtain resource and location information for resource management applications. Resource management applications are typically run at least in part using computers connected over a LAN. As an example, an aircraft is being assembled in a hangar. Information regarding each part both before and after assembly is collected using an RFID system and the information is collected using a computer resource management (CRM) application running on computers interconnected within the hangar using a wired LAN. Use of a wireless LAN in the hangar may be limited because of mutual RF interference between the RFID (UWB) network and the wireless LAN.
Thus, there is a need for and it would be advantageous to have WLAN and RFID system based on ultra wide operating in the same space without interfering with each other so that portable computers interconnected with a wireless LAN may be operated in the same space as the RFID/UWB network.
In FIG. 7, a graph illustrates schematically different emitted signal power levels including an ultra-wide band signal, a spread spectrum WLAN (Institute of Electrical and Electronics Engineers, IEEE 802.11a) signal with bandwidth about 5 MHz, and a narrow band modulated signal of 30 kHz bandwidth. The noise floor of the spread spectrum WLAN signal is illustrated at about the peak signal level of the ultra-wide band signal indicating that the narrow band and spread spectrum WLAN communications should have little difficulty operating within specifications in the presence of UWB signals. However, an RFID system using ultra wide band signaling is susceptible to receive high signal levels (up to for instance 18 dbm) from a WLAN operating in the same vicinity as the RFID/UWB network.
The term “ultra-wide band” (UWB) as used herein is defined (by FCC and ITU-R) in terms of a transmission from an antenna for which the emitted signal bandwidth exceeds the lesser of 500 MHz or 20% center frequency. Ultra-wide band (UWB) communication technology employs discrete pulses of electromagnetic energy that are emitted at, for example, picosecond to microsecond intervals. For this reason, ultra-wide band is often called “impulse radio.” A UWB pulse is a single electromagnetic burst of energy. A UWB pulse can be either a single positive burst of electromagnetic energy, or a single negative burst of electromagnetic energy, or a series of pulses. Each pulse in al pulse-based UWB system occupies the entire UWB bandwidth, e.g. 3.1 to 10.6 GHz. thus having relative immunity to multipath fading (but not to intersymbol interference), unlike carrier-based systems that are subject to both deep fades and intersymbol interference. Ref: http://en.wikipedia.org/wiki/Ultra_wide band.
WLANs are local area networks that employ high-frequency radio waves rather than wires to exchange information between devices. IEEE 802.11 refers to a family of WLAN standards developed by the IEEE. In general, WLANs in the IEEE 802.11 family provide for 1 or 2 Mbps transmission in the 2.4 GHz band or 5.2 Ghz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) transmission techniques. IEEE 802.11b (also referred to as 802.11 High Rate or Wi-Fi) is an extension to IEEE 802.11 and provides for data rates of up to 11 Mbps in the 2.4 or 5 GHz band providing wireless functionality comparable to Ethernet. IEEE 802.11b employs only DSSS transmission techniques. IEEE 802.11g provides for data rates of up to 54 Mbps. For transmitting data at rates above 20 Mbps, IEEE 802.11g employs Orthogonal Frequency Division Multiplexing (OFDM) transmission.
In order to reduce the probability of two stations colliding on a receiver because they cannot hear each other, the IEEE 802.11 standard uses a Request to Send/Clear to Send (RTS/CTS) handshake. A station requiring to transmit a packet first transmits a short control packet called RTS (Request To Send), which includes the source, destination, and the duration of the following frame; the target station replies (if the medium is free) with a control packet called CTS (Clear to Send), which includes the same duration information. All stations receiving either the RTS and/or the CTS, refrain transmission for the given duration. This mechanism reduces the probability of a collision on the receiver area by a station that is “hidden” from the transmitter (and it does not hear the RTS), since the station hears the CTS and “reserves” the medium as busy until the end of the transmission. The duration information on the RTS also protects the transmitter area from collisions during the ACK (from stations that are out of range of the acknowledging station).
IEEE 802.11e as of late 2005 has been approved as a standard that defines a set of Quality of Service enhancements for LAN applications, in particular the 802.11 WiFi standard. The standard is considered of critical importance for delay-sensitive applications, such as Voice over Wireless IP and Streaming Multimedia. The protocol enhances the IEEE 802.11 Media Access Control (MAC) layer.
The basic 802.11 MAC layer uses the Distributed Coordination Function (DCF) to share the medium between multiple stations. DCF relies on Carrier Sense Multiple Access With Collision Avoidance (CSMA/CA) and optional 802.11 RTS/CTS to share the medium between stations.
The original 802.11 MAC defines another coordination function called the Point Coordination Function (PCF): this is available only in “infrastructure” mode, where stations are connected to the network through an Access Point (AP). Access points send “beacon” frames at regular intervals (usually every 0.1 second). Between these beacon frames, PCF defines two periods: the Contention Free Period (CFP) and the Contention Period (CP). In CP, the DCF is simply used. In CFP, the access point sends Contention Free-Poll (CF-Poll) packets to each station, one at a time, to give them the right to send a packet.
The 802.11e enhances the DCF and the PCF, through a new coordination function: the Hybrid Coordination Function (HCF). Within the HCF, there are two methods of channel access, similar to those defined in the legacy 802.11 MAC: HCF Controlled Channel Access (HCCA) and Enhanced DCF Channel Access (EDCA). Both EDCA and HCCA define Traffic Classes (TC). For example, emails could be assigned to a low priority class, and Voice over Wireless IP (VoWIP) could be assigned to a high priority class.
With EDCA, high priority traffic has a higher chance of being sent than low priority traffic: a station with high priority traffic waits a little less before it sends its packet, on average, than a station with low priority traffic. In addition, each priority level is assigned a Transmit Opportunity (TXOP). A TXOP is a bounded time interval during which a station can send as many frames as possible (as long as the duration of the transmissions does not extend beyond the maximum duration of the TXOP). If a frame is too large to be transmitted in a single TXOP, it should be fragmented into smaller frames. The use of TXOPs reduces the problem of low rate stations gaining an inordinate amount of channel time in the legacy 802.11 DCF MAC.
Wi-Fi Multimedia (WMM) certified APs must be enabled for EDCA and TXOP. All other enhancements of the 802.11e amendment are optional.
The HCCA functions similarly to PCF: the interval between two beacon frames is divided into two periods, the contention free period (CFP) and the contention period (CP). During the CFP, the Hybrid Coordinator (HC) e.g. the access point, controls the access to the medium. During the CP, all stations function in EDCA. The main difference with the PCF is that Traffic Classes (TC) are defined. The HC can coordinate the traffic in any fashion it chooses (not just round-robin). Moreover, the stations give info about the lengths of their queues for each Traffic Class (TC). The HC can use this info to give priority to one station over another. Another difference is that stations are given a TXOP: they may send multiple packets in a row, for a given time period selected by the HC. During the CP, the HC allows stations to send data by sending CF-Poll frames.
HCCA is generally considered the most advanced (and complex) coordination function. With the HCCA, QoS can be configured with great precision. QoS-enabled stations have the ability to request specific transmission parameters (data rate, jitter, etc.) which should allow advanced applications like VoIP and video streaming to work more effectively on a Wi-Fi network
The term “frequency division” as used herein is a method to achieve radio frequency isolation between two RF communications systems or channels by separating the radio frequencies in use by the systems or channels.
The term “co-exist or co-existence” in the context of radio frequency systems, refers to the ability of the radio frequency systems to operate according to their respective specifications without interfering with each other typically by causing noise and/or distortion to each other.
The term “time division” as used herein is a method to achieve co-existence between two RF systems or channels by having the systems or channels operate in different time slots.                (Ref. http://en.wikipedia.org/wiki/IEEE—802.11e)        
A known technique used to provided co-existence of different wireless networks is known as “detect and avoid”. An example of “detect and avoid” is found in international patent application of Palin et al. (WO/2005/119924) entitled “Method and System for Interference Detection”. Palin et al. disclose a wireless communications device in which static interference is detected so that frequencies in use are avoided. The system includes a first receiver configured to receive a first wireless signal (such as a Bluetooth or WLAN signal), and a second receiver configured to receive a second wireless signal (such as a UWB signal). The second receiver is configured to determine spectral characteristics of the first wireless signal. Based on these determined spectral characteristics, an interference detection module identifies interference in the first wireless signal.